Method of desulfurization by treatment with elemental halogens



Patented Apr. 11, 1950 METHOD OF DESULFURIZATION BY TREAT- MENT WITH ELEMENTAL HALOGEN S Chester M. Himel, Bartlesville, Okla, asslgnor to Phillips Petroleum Company, a corporation of Delaware No Drawing. Application August 7, 1947,

Serial No. 767,359

hydrocarbons. In a more specific aspect it relates to a process for the removal of disulfides from normally liquid saturated hydrocarbons wherein the said hydrocarbon is subjected to treatment with elemental halogen.

In the refining of crude petroleum oils various sulfur compounds such as hydrogen sulfide, mercaptans, thioethers, disulfides, thiophenes, cyclic polymethylene sulfides, and the like are encountered in the charging stocks. These substances impart objectionable characteristics to the products such as disagreeable odor, corrosiveness to metal surfaces, en ine knock, instability to light, etc., and numerous methods have been developed by which most of them can be removed or transformed into less deleterious compounds. In one wide y used process employed in the manufacture of gasoline, residual mercaptans are oxidized to disulfides in order to eliminate their obnoxious odor. Since the concentration of disulfides so produced together with those previously in the charge stock is generally relatively small, they are usually allowed to remain in the product, their removal by methods heretofore known being laborious and expensive and often inefilcient.

However, the presence of disulfides is known to have a depressing effect on lead response in motor fuels, and may in some instances, render the product unsuitable for such use, particularly when employed as a blending stock in the manufacture of high octane gasolines. Furthermore it is often desirable to produce pure hydrocarbons for specialized purposes from petroleum fractions and the presence of disulfides, even in small amounts, in such products is obviously objectionable. From these considerations it is apparent that an efiicient and economical means for the removal of disulfides from hydrocarbons has a high degree of significance in the petroleum industry.

It is an object of the present invention to provide a process for the substantially complete removal of alkyl disulfides from hydrocarbons containing the same. It is a further. object of the invention to efiect the removal of mercaptan sulfur from hydrocarbons containing the same by a combination process in which disulfides are first formed from the mercaptans and then removed by chemical reaction and solution. Further objects will be apparent from the disclosure herein.

I have now discovered a process for the removal of disulfides from normally liquid saturated hydrocarbons whereby subs tially complete separation is effected, opera 11 Claims, (c1.19e-z4) us are rapid 55 and easily carried out, and costs are economically advantageous. According to the process of my invention the hydrocarbon or hydrocarbon fraction is treated with elemental halogen under conditions for substantially complete conversion of constituent disulfides to the corresponding sulfenyl halides which are subsequently removed by washing with an aqueous alkaline solution, such as a solution containing sodium or potassium hydroxide.

The efilciency of the present process results from the rapid and essentially complete reaction of halogen with the sulfur atoms of the disulfid'e' with substantially no halogenation of other parts of the molecule or of the hydrocarbon. When operating in this manner the disulfide content of a saturated hydrocarbon or mixture of such hydrocarbons can be substantially completely removed or reduced to negligible proportions. A particularly significant feature of the present invention lies in its applicability to the removal of small concentrations of disulfides such as are found in commercially produced petroleum fractions. For example in a hydrocarbon sample con taining 0.1 per cent of disulfide the application of the present method will reduce the disulfide content to 0.001 per cent or less, a negligible concentration.

A further advantage of my process lies in the simplicity and ready adaptability to existing equipment. For example, by operating the fractionating system in which a gasoline is distilled at pressures such that temperatures are main-' tained at the optimum level for the reaction of the present invention, disulfides can be removed from both the overhead and the kettle product by introduction of the calculated amount of chlorine into the kettle during the fractionations. By so operating, constituent disulfides are'converted to sulfenyl halides which either remain in thekettle product or are decomposed to sulfur, hydrogen chloride or other easily removable mate! rials, thus yielding a; disulfide-free overhead fraction. By discharging the-kettle product into a A caustic wash the sulfenyl halides are removed in the aqueous phase. Thus disulflde removal is effected in the total product, both'from the overhead fraction or fractions and the higher boiling residues in. a single operation with the employment of conventional equipment. In another embodiment of my process appli-- cable to the removal of disulfides as a step in the production of pure hydrocarbons the halogen is fed into the hydrocarbon in a tube furnace oper-, ated at a temperature favorable to the reaction? The eiiluent is then discharged to a camtic washing step as before, thus effecting the removal of constituent disulfldes without fractionation of the product. When so operating pressures in the heating coils of the furnace are maintained at a level such that liquid phase conditions are preserved at the reaction temperature.

Temperatures in the reaction zone will generally be maintained between 20 and 250 F., preferably between 80 and 150 F. but in any case will not be suiliciently high for chlorination of the hydrocarbon. Pressures will be maintained at levels such that at least mixed phase operation is insured. When treatment is effected during fractionation, the reflux is maintained at a ratio such that conversion of disuliides is completed in the tower. As previously mentioned, treatment in reactors or heating coils such as in a tube furnace is effected under sufficient pressure to insure the preservation of liquid or at least mixed phase conditions at the optimum operating temperature. v.

Hydrolysis and solution of the sulfenyl halide can be markedly hastened by the use of hot caustic solutions for washing. When so operating it may be desirable to conduct the washing process under suiilcient pressure to avoid vaporization losses from the hydrocarbon. Obviously washing with water will be employed to remove traces of caustic before the hydrocarbon is stored.

While bromine and iodine can be employed for the removal of disuliides in my process, I have preferred to use chlorine due to its normally gaseous state, its low cost, and rapid action. Also, by operating in this manner, any residual halogen remaining in the hydrocarbon after treatment is readily removed in the caustic and subsequent washing of the product. While I have preferred to introduce the chlorine as a gas it may, when desired, be added in the liquid state.

The amount of halogen added will be determined by the disulfide content of the hydrocarbon treated. In general I have preferred to employ a slight excess over the theoretical amount, say about ten per cent. Thorough admixture of the halogen with the hydrocarbon is desirable and can be effected by a centrifugal pump, turbomixer, high speed jet, or similar device in the feed line. When the reaction is carried out in a fractionating tower the refluxing hydrocarbon oifers additional opportunity for contact with the halogen.

While the process of the present invention has been disclosed with particular reference to the removal of disulfides, it may be extended to the removal of mercaptans, either by first oxidizing the mercaptans to disuliides by any suitable means, such as for example, a copper sweetening process, and subsequent treatment of the product with elemental halogen, or by direct halogenation by which means the mercaptans may be converted directly to sulfenyl halides and removed in the above described manner. Such application of my process is within the scope of this disclosure.

The present invention, therefore provides a process for the removal of disulfides from saturated hydrocarbons in which the hydrocarbon is treated with an elemental halogen selected from the class consisting of chlorine, bromine, and iodine. Fluorine has not been shown to be very satisfactory for this pur ose because of its reactivity with saturated hydrocarbons and in view of the fact that complex sulfur-halogen compounds are formed which cannot be readily removed by washing as is the case with the alkyl sulfenyl halides formed by the other halogens. The reaction should be carried out in the substantial absence of water, other than such small amounts as may be normally present dissolved in the hydrocarbon.

The specific disulndes or mixtures thereof, which are reacted in the manner described, will vary in accordance with the nature and boiling point of the hydrocarbon being treated. This will inturn be related to the mercaptans originally present prior to the sweetening treatment. In the case of a natural gasoline which has been debutanized, the mercaptans likely to be present would include methyl mercaptan, ethyl mercaptan, nand ipropyl mercaptan, nand ibutyl mercaptan, and the amyl and hexyl mercaptans, etc. During the sweetening process these mercaptans are oxidized to the corresponding disuliides, and the final product, if redistilled, would contain the disulfides boiling in the range of the gasoline or fraction thereof which is recovered.

EXAMPLES A sample of n-pentane containing 0.175 per cent of mixed disulfldes including dimethyl and diethyl disulfides was placed in a reaction vessel fitted with a reflux condenser. The temperature was raised until the pentane was refluxing gently at which time a stream of gaseous chlorine was admitted at. a rate such that its absorption was substantially complete. When an amount of chlorine equivalent in mols to the disulflde content had been introduced, a small excess was added and the system maintained at reflux for a few minutes. The mixture was then poured into an equal volume of a ten per cent sodium hydroxide solution and agitated for 45 minutes to hydrolyze and dissolve the sulfenyl halides. After standing a few minutes to :permit separation of the phases the hydrocarbon layer was removed, washed twice with water and dried over anhydrous calcium chloride. Analysis of the product showed a disulfide content of less than 0.001 per cent.

A quantity of normal hexane containing 0.201 per cent of disuliides including dimethyl and diethyl disulfides was introduced into a tube furnace through a pipe equipped with a high speed jet for introduction of chlorine gas into the stream and a centrifugal pump to further insure thorough admixture of the chlorine with the hydrocarbon. Temperature in the furnace was maintained at :5 F. The emuent stream was discharged into a tube where it was commingled with a ten per cent sodium hydroxide solution by the action of a second centrifugal pump operating to provide a pressure of 100 pounds :per square inch gauge, the temperature of the caustic solution being 200 F. The mixture was discharged to a settler from which the hydrocarbon layer was conveyed to washing tanks and agitated with water for removal of traces of caustic. The dried product was found to contain approximately 0.001 per cent of disuliide.

III

Natural gasoline containing 0.195 per cent of disulfides and which had previously been sweetened by conventional solid copper treating to convert the mercaptans to disuliides, was introduced into a fractionating tower operated at pressures such that the desired fractions were separated at temperatures below 200 F. Gaseous chlorine was passed into the kettle at a rate such that substantially no free chlorine appeared in the overhead. Both the overhead fractions and the kettle product were subjected to caustic washing at 200. F. and 100 pounds per square inch pressure after which they were washed with water.

-Disulflde content of the products was negligible,

being less than 0.002.

I claim:

1. A process for the desulfurization of a normall liquid saturated hydrocarbon containing alkyl disuifldes which comprises contacting said hydrocarbon with elemental halogen selected from the group consisting of chlorine, bromine and iodine, at a temperature in the range of to 250 F. and below that at which halogenation of the hydrocarbon is effected thereby converting said disulfides to the corresponding alkyl sulfenyl halides, and separating said alkyl sulfenyl halides from said hydrocarbons.

2. A process according to claim 1 wherein the alkyl sulfenyl halides are separated by washing with an aqueous alkaline solution.

3. A process according to claim 2 wherein the halogen is chlorine. v

4. A process for the removal of alkyl disulfide impurities from a normall liquid saturated hydrocarbon which comprises "contacting said hydrocarbon with elemental halogen selected from the group consisting of chlorine, bromine and iodine, at a temperature in the range of 20 to 250 F. and below that at which any substantial halogenation of the hydrocarbon is eifected to form the corresponding alkyl sulfenyl halide by reaction of said disulfide with said halogen, and washing the reaction mixture with an aqueous alkaline solution to remove said alkyl sulfenyl halide therein.

5. A process according to claim 4 wherein the halogen is chlorine.

6. A process according to claim 4 wherein the halogenation reaction is carried out during distillation of the hydrocarbon by introducing the halogen into the distillation column, effecting reaction of said disulfides therein and separat overhead a disulflde-free product.

7. A process according to claim 6 wherein the alkyl sulfeny1 halides formed are concentrated in the kettle product and are removed by washing with aqueous alkaline solution.

8. A process for the removal of mercaptan sulfur from normally liquid saturated hydrocarbons containing mercaptans as impurities which comprises oxidizing said mercaptans to form the corresponding disulfldes, converting said disulfldes to alkyl sulfenyl halides by contact with elemental halogen selected from the group consisting of chlorine, bromine and iodineat a temperature in the range of 20 to 250 F. and below that at which halogenation of the hydrocarbon is effected, and removing the resultant alkyl sulfenyl halides by washing with an aqueous alkaline solution.

9. A process according to claim 8 wherein the halogen is chlorine.

10. A process according to claim 9 wherein the mercaptans are oxidized by contact with cupric chloride.

11. A process for the removal of mercaptan sulfur from normally liquid saturated hydrocarbons containing mercaptans as impurities which comprises contacting said hydrocarbons with elemental halogen selected from the group consisting of chlorine, bromine and iodine, at a temperature in the range of 20 to 250 F. and below that at which substantial halogenation of the hydrocarbon is affected to form the corresponding alkyl sulfenyl halide, and removing said alkyl sulfenyl halide from the reaction mixture.

CHESTER M. HIMEL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Great Britain Apr. 25, 1922 

1. A PROCESS FOR THE DESULFURIZATION OF A NORMALLY LIQUID SATURATED HYDROCARBON CONTAINING ALKYL DISULFIDES WHICH COMPRISES CONTACTING SAID HYDROCARBON WITH ELEMENTAL HALOGEN SELECTED FROM THE GROUP CONSISTING OF CHLORINE, BROMINE AND IODINE, AT A TEMPERATURE IN THE RANGE OF 20 TO 250*F. AND BELOW THAT AT WHICH HALOGENATION OF THE HYDROCARBON IS EFFECTED THEREBY CONVERTING SAID DISULFIDES TO THE CORRESPONDING ALKYL SULFENYL HALIDES, AND SEPARATING SAID ALKYL SULFENYL HALIDES FROM SAID HYDROCARBONS. 